Re: [PATCH] Add MOUNT_STATUS ioctl to cdrom device

[viro@parcelfarce.linux.theplanet.co.uk]

On Tue, Aug 26, 2003 at 01:22:37AM +0700, Samphan Raruenrom wrote:
> Hi,
> 
> This patch add a new ioctl MOUNT_STATUS to the 2.4 kernel's cdrom
> device. It'll be used as an API to query the mount status of a
> cdrom :-
> 
> CDROM_MOUNT_STATUS
> Return :-
> 0 = not mount.
> 1 = mounted, but not in-use. It is ok to umount.
> 2 = busy. Umount will result in getting EBUSY.
> <0 = error.

Huh?   And what, pray tell, makes cdrom special?  Not to mention
the use of ioctl, the inherent raciness of the interface and the fact
that yes,
 
> This same functionality can be done in user-space,

... which should be the end of it.

> +	case CDROM_MOUNT_STATUS: {
> +		struct super_block *sb = get_super(dev);
> +		if (sb == NULL) return -EINVAL;
> +		down_read(&current->namespace->sem);
> +		struct vfsmount *mnt = NULL;
> +		struct list_head *p;
> +		list_for_each(p, &current->namespace->list) {
> +			struct vfsmount *m = list_entry(p, struct vfsmount, 
> mnt_list);
> +			if (sb == m->mnt_sb) {
> +				mnt = m; break;
> +			}
> +		}
> +		up_read(&current->namespace->sem);		

And what about other namespaces?

> +		drop_super(sb);		
> +		int mstat = 0; /* 0 not mounted, 1 umount ok, 2 umount EBUSY 
> */
> +		if (mnt) mstat = 1 + (atomic_read(&mnt->mnt_count) > 1);

Or the possibility that
	* mnt might've been freed by that point.
	* we might have the damn thing mounted in several places, some
busy, some not.
	* cdrom had been used not by mount.
	* cdrom had been mounted just as we had decided to tell that it's
not busy.